Companies advertise BPA-free plastic as a safer version of products ranging from water bottles to sippy cups to toys. Many manufacturers stopped using bisphenol A, a chemical that is used to strengthen plastic, after studies linked it to early puberty and a rise in breast and prostate cancers. However, bisphenol S, or BPS, a common replacement for BPA in plastics, also has been linked to health risks. New UCLA-led research demonstrates some of the mechanisms that make BPS just as harmful as BPA. The study found that BPS speeds up embryonic development and disrupts the reproductive system in animals.

“Our study shows that making plastic products with BPA alternatives does not necessarily leave them safer,” says Nancy Wayne, PhD, professor of physiology and associate vice chancellor for research. “The findings are frightening. Consider it like the canary in the coal mine.”

Dr. Wayne and her colleagues found that when zebrafish were exposed to either BPA or BPS at low levels — equivalent to the traces found in polluted river waters — their physiology at the embryonic stage changed in as quickly as 25 hours. “Egg-hatching time accelerated, leading to premature birth,” Dr. Wayne says. “The embryos developed much faster than normal in the presence of BPA or BPS.”

The research team studied zebrafish because their transparent embryos make it relatively easy to “watch” cell growth as it occurs. Using fluorescent-green protein tags, the researchers tracked the development of the animals’ reproductive endocrine brain cells, which control puberty and fertility. They discovered that the number of endocrine neurons increased up to 40 percent, suggesting that BPA overstimulates the reproductive system. “We saw many of these same effects with BPS found in BPA-free products. BPS is not harmless,” Dr. Wayne says.

The researchers also were surprised to find that both BPA and BPS exert their effects partly through an estrogen system and partly through a thyroid-hormone system. “Most people think of BPA as mimicking the effects of estrogen,” Dr. Wayne says. “But our work shows that it also mimics the actions of thyroid hormone.”

Thyroid hormone has a significant influence on brain development during gestation, so the research could have important implications for understanding general embryonic and fetal development, including in humans. Researchers have proposed that endocrine-disrupting chemicals may be contributing to the rise in premature human births and early onset of puberty over the past couple of decades in the U.S. “Our data support that hypothesis,” Dr. Wayne says. “If BPA is affecting a wide variety of animal species, then it’s likely to be affecting human health.”

BPA can leach into food and beverages, particularly under heat, from cans, baby bottles, food-storage containers and plastic tableware. It also can be found in contact lenses, eyeglass lenses, compact discs, water-supply pipes, cash register and ATM receipts and dental sealants and composites. One study published in 2010 projected that by 2015, the U.S. and Europe would be manufacturing more than 5-million tons per year of products containing BPA.

Actions of Bisphenol A and Bisphenol S on the Reproductive Neuroendocrine System during Early Development in Zebrafish,” Endocrinology, December 10, 2015